The present invention relates generally to printed circuit boards, such as those commonly used to facilitate electrical interconnection of components in electronic assemblies. The present invention relates more particularly to integrally formed electrical interconnects for printed circuit boards. The electrical interconnects may be configured so as to either provide electrical communication between a plurality of printed circuit boards or so as to define terminations for such printed circuit boards. The electrical interconnects may additionally be configured to define electrical connectors. The present invention also comprises a method for forming such electrical interconnects.
Electrical interconnections for facilitating electrical communication between printed circuit boards are well known. Typically, printed circuit boards are electrically interconnected either via flexible conductors, i.e., cables, or via rigid conductors such as the traces of a printed circuit board bus. The use of cables is advantageous in that cables facilitate electrical communication between printed circuit boards having various different orientations with respect to one another. For example, two printed circuit boards may be oriented parallel to one another, perpendicular to one another, or at any other desired relative angle or orientation, when electrically interconnected via cables.
However, the use of such flexible conductors generally requires that cable connectors be fabricated or purchased and then attached, e.g., soldered, to each of the printed circuit boards and that cables with complimentary connectors also be provided. Thus, such electrical interconnection of printed circuit boards via flexible conductors suffers from the inherent disadvantage of increased cost due to the substantial costs of materials and labor associated therewith.
Further, cables do not typically provide a robust electrical connection, i.e., an electrical connection which is desirably reliable and effective. As those skilled in the art will appreciate, the connectors utilized to attach such cables to printed circuit boards inherently introduce substantial problems. The electrical connection of a cable to the complimentary cable connector of a printed circuit board may not be either reliable or effective for several reasons. Mechanical contact between the individual electrical contact members, e.g., pins and sockets, of such cable connectors may not be sufficient to provide the desired electrical connection therebetween. As those skilled in the art will appreciate, good mechanical contact between the electrical contact members of cable connectors is necessary in order to provide the desired electrical interconnection. Poor mechanical contact may be due to poor design and/or bending of the contacts during handling. Further, wear of the electrical contacts due to repeated attachment and detachment of the electrical connectors also commonly results in such poor mechanical contact.
Further, such electrical contacts are subject to degradation caused by environmental factors, such as moisture, air pollutants and soiling. Such degradation of the electrical contracts frequently results in the formation of a high resistance layer thereupon, which substantially inhibits the flow of electric current therethrough. Thus, such degradation of the electrical contacts frequently renders the electrical contracts unsuitable for the reliable transmission of electrical signals. As those skilled in the art will appreciate, even when handled and assembled properly, the reliability of electrical cable connectors is substantially lower than desirable.
Printed circuit board buses for rigidly interconnecting a plurality of separate printed circuit boards are also well known. A common example of such a printed circuit board bus is the ISA/PCI bus of a contemporary IBM compatible personal computer (PC) which is utilized to interconnect a plurality of different printed circuit board add-on cards, such as a display adaptor, a sound card, and/or a modem card with the central processing unit (CPU) and the random access memory (RAM) of the personal computer. Such printed circuit board buses comprise a plurality of female card edge connectors which are rigidly attached to the printed circuit board, i.e., the motherboard of the personal computer. The add-on cards attach to the female card edge connectors via complimentary male card edge connectors formed of conductive traces at an edge of each add-on card. A plurality of conductive conduits or traces extend in a generally parallel fashion between the female card edge connectors and provide electrical communication therebetween.
Although such rigid printed circuit board buses may be somewhat more reliable than flexible cables, since relative movement between the printed circuit boards attached thereby is inhibited by such rigid attachment of the boards to one another, the printed circuit boards attached to such a printed circuit board bus must generally be oriented approximately parallel to one another and must be oriented approximately perpendicular to the printed circuit board upon which the bus is formed. Thus, the physical layout of such printed circuit boards is undesirably constrained. Further, such bus connectors suffer from some of the same inherent deficiencies as cable connectors, i.e., they are subject to degradation caused by moisture, air pollutants and soiling, as well as by handling and wear.
It is desirable to be able to orient printed circuit boards at various different angles with respect to one another. For example, in some instances it may be desirable to provide electrical communication between printed circuit boards which are oriented such that they are parallel to one another. This may be done to minimize the space occupied by the printed circuit boards. In other instances, it may be desirable to provide electrical communication between printed circuit boards which are oriented such that they are perpendicular to one another. They may be done so that each printed circuit board can be mounted to each one of two adjacent perpendicular walls of a rectangular enclosure, for example.
It may even occasionally be desirable to orient printed circuit boards at other desired angles or orientations relative to one another in order to accommodate packaging requirements. For example, it may be necessary to orient one printed circuit board at an angle of approximately 45 degrees with respect to the other printed circuit board in order to accommodate the desired packaging of large components, e.g., transformers, mounted to or near one or both of the printed circuit boards. That is, such large components may prevent orientation of the printed circuit boards parallel to one another and may similarly prevent mounting of a printed circuit board close to the perpendicular walls of an enclosure and thus prevent mounting of the printed circuit boards perpendicular to each other.
In view of the foregoing, it is desirable to provide robust electrical interconnects between printed circuit boards which are oriented at substantially any desired angle with respect to one another.
Additionally, it is frequently desirable to piggyback a small printed circuit board to a larger printed circuit board. This frequently occurs when, for example, the smaller printed circuit board defines a multi-chip module or contains hybrid circuitry, i.e., a combination of discrete and integrated circuit components, and is to be placed in electrical communication with a larger printed circuit board. One common example of such attachment of a small printed circuit board to a larger printed circuit board is the attachment of a random access memory (RAM) module to a personal computer motherboard. Such attachment is typically accomplished by providing a connector (such as a SIMM connector) on the larger printed circuit board for receiving complimentary leads or terminations from the smaller printed circuit board.
Such terminations typically comprise a plurality of pins permanently attached to the smaller printed circuit board and in electrical communication with the electrical components of the smaller printed circuit board. The fabrication of a printed circuit board having pins for facilitating electrical interconnection with another, typically larger, printed circuit board is inherently labor intensive, since holes must typically be drilled in the printed circuit board to receive the pins, the pins must be inserted into the holes and the pins must be soldered in place.
Alternatively, male card edge connectors may be formed upon the smaller printed circuit board and configured to attach to a complimentary female card edge connector which is attached to the larger printed circuit board. Such male card edge connectors comprise a plurality of conductive traces or terminations formed upon a desired edge of the printed circuit board. The traces define parallel fingers that extend to the edge of the printed circuit board and are perpendicular thereto. The parallel finger terminations of a male card edge connector are received within a female card edge connector attached to another, typically larger, printed circuit board and electrical contact is made to the parallel finger terminations of the male card edge connector via spring contacts within the female card edge connector. Such card edge connectors are commonly used to attach add-on daughter cards to the motherboard of an IBM compatible personal computer, for example.
However, as those skilled in the art will appreciate, such contemporary card edge connector terminations suffer from inherent deficiencies. The disadvantages associated with the use of connectors, as discussed above, apply to such card edge connectors. Further, the use of such card edge connectors is limited to generally perpendicular mounting of the printed circuit boards. As those skilled in the art will appreciate, perpendicular mounting is not suitable for all applications. In some instances, packaging requirements dictate that parallel mounting of the printed circuit boards relative to one another be utilized instead. Indeed, packaging requirements may dictate that two printed circuit boards be oriented at various different angles with respect to one another, as discussed above.
It is desirable to provide robust electrical terminations for electrically connecting a printed circuit board or the like to another printed circuit board or to an electrical connector, wherein the terminations are defined integrally with conductive traces formed upon the printed circuit board, so as to reduce manufacturing costs and enhance the reliability thereof.
The present invention specifically addresses and alleviates the above-mentioned deficiencies associated with the prior art. More particularly, the present invention comprises a method for forming electrical interconnects for printed circuit boards and the like. The interconnects comprise either a plurality of electrical conduits which fixedly attach one printed circuit board to another printed circuit board or conductive conduits (such as terminations) which removably attach one printed circuit board to another printed circuit board or to a cable connector or the like.
The method comprises the steps of laminating a first surface of a rigid dielectric substrate with a first conductive laminate such that the first conductive laminate extends beyond at least one edge of the dielectric substrate (such as an edge defined by a window formed in the dielectric substrate), patterning the first conductive laminate to define a plurality of electrical interconnects which extend beyond the edge(s) of the dielectric substrate, forming a plurality of conductive traces on a second surface of the dielectric substrate and forming a plurality of openings in the dielectric substrate to define vias for electrically interconnecting the interconnects and the conductive traces.
The interconnects, the conductive traces, and the vias may be formed in any desired order. The interconnects facilitate attachment of the printed circuit board to another printed circuit board or to a connector, as discussed in detail below. The conductive traces facilitate electrical communication between electronic components formed upon the printed circuit board, as is common in the art.
Each of the openings extends from a first location on a first surface of the dielectric substrate which is proximate at least one electrical interconnect to a second location on the second surface of the substrate which is proximate at least one conductive trace. Conductive material is formed within the openings of the dielectric substrate such that vias are formed wherein the conductive material facilitates electrical communication between the electrical interconnects formed upon the first surface of the substrate and the conductive traces formed upon the second surface of the substrate.
The step of forming the plurality of conductive traces on the second surface of the dielectric substrate preferably comprises laminating the second surface of the dielectric substrate with a second conductive laminate and patterning the second conductive laminate to define the conductive traces. The conductive traces may alternatively be formed upon the second surface of the dielectric substrate by sputtering, vapor deposition, electroplating or by any other desired process.
Preferably, at least one window is formed within the dielectric substrate and the step of laminating the first surface of the dielectric substrate such that the first conductive laminate extends beyond at least one edge of the dielectric substrate comprises laminating the first surface of the substrate such that the first conductive laminate extends across the window(s). The first conductive laminate thus extends beyond an edge of the dielectric substrate which defines an edge of the window.
The step of forming at least one window(s) in a dielectric substrate preferably comprises forming a window in a dielectric substrate having a layer of conductive material (such as the second conductive laminate) formed upon the second surface thereof such that the window(s) are formed in both the dielectric substrate and the layer of conductive material simultaneously, wherein the conductive traces are subsequently formed from the conductive layer. The step of forming a window in the dielectric substrate preferably comprises dye cutting the window into the dielectric substrate (and simultaneously cutting the window into the layer of conductive material).
Alternatively, the window(s) are formed separately in each of the dielectric substrate and the second conductive laminate, prior to laminating the second surface of the dielectric substrate with the second conductive laminate. Of course, forming window(s) in the dielectric substrate and the second conductive laminate separately necessitates that the window(s) be aligned to one another, prior to laminating the dielectric substrate with the second conductive laminate.
As a further alternative, a window is not formed in the second conductive laminate until a later etching step, wherein conductive traces are also formed from the second conductive laminate.
The steps of patterning the first and second conductive laminates preferably comprise applying resist to the first and second laminates and then acid etching the first and second laminates.
The step of laminating the first surface and the step of forming a plurality of conductive traces on the second surface preferably comprise laminating the first surface with a laminate having a thickness which is different from a thickness of the conductive traces. The laminate of the first surface preferably has a greater thickness than the conductive traces of the second surface. By laminating the first surface with a laminate having a thickness greater than the thickness of the conductive traces, interconnects are formed from the laminate of the first surface which are thicker, and therefore more durable than the conductive traces formed upon the second surface. This is particularly important when the interconnects are to be bent, as when orienting to printed circuit boards at a desired angle relative to one another.
The step of laminating the first surface with a conductive laminate comprises laminating the first surface with a sheet material comprising a substance such as copper, beryllium copper, nickel or brass. The step of forming a plurality of conductive traces on the second surface of the dielectric substrate preferably comprises laminating the second surface of the substrate with a sheet material comprising a substance such as copper, beryllium copper, nickel or brass.
According to the preferred embodiment of the present invention, both the first and second surface of the dielectric substrate are laminated with a conductive material which is attached thereto by adhesive.
The plurality of electrical interconnects may be formed so as to extend between at least two printed circuit boards, so as to facilitate electrical communication between the printed circuit boards. The electrical interconnects may be bent so as to orient the two printed circuit boards at a desired relative position with respect to one another. Thus, the two printed circuit boards may be oriented perpendicular to one another, parallel to one another, or at any other desired angle with respect to one another. When the electrical interconnects are bent such that the two electrical printed circuit boards are generally parallel to one another, the electrical interconnects which connect the two printed circuit boards may optionally be used as a connector, as discussed in detail below.
The step of patterning the first conductive laminate to define a plurality of electrical interconnects optionally comprises patterning the first conductive laminate to define a thermal management interface as well.
The plurality of electrical interconnects may be formed so as to extend from a single printed circuit board (rather than fixedly interconnecting two separate printed circuit boards), so as to define terminations for the printed circuit board. Such terminations may, for example, extend from the printed circuit board such that they are generally perpendicular thereto, similar to the manner in which the legs extend from a dual in-line package (DIP) integrated circuit (IC) chip. Thus, the printed circuit board may be attached to another printed circuit board, via either a socket or directly, in much the same manner that a DIP IC is attached to a printed circuit board.
The terminations may extend from the printed circuit board such that they can be inserted into complimentary holes formed in another printed circuit board, so as to effect electrical interconnection of the two printed circuit boards, as discussed in detail below.
The terminations may optionally be bent into a generally xe2x80x9cUxe2x80x9d shape so as to enhance use of the terminations with connectors. Such bending of the terminations into a xe2x80x9cUxe2x80x9d shape increases the structural strength of terminations defined thereby, so as to enhance the reliability thereof. The terminations are preferably bent over a spacer. The spacer optionally comprises the same dielectric material which defines the rigid dielectric substrate.
Alternatively, the terminations may be bent into a gull wing configuration, so as to enhance use of the conductive conduits in surface mount applications. As those skilled in the art will appreciate, such a gull wing configuration provides greater surface area for mounting, thereby enhancing the reliability thereof.
Thus, according to the present invention, an electrical interconnect facilitates electrical communication between two printed circuit boards, either by fixedly attaching two printed circuit boards to one another or by defining a termination which facilitates detachable attachment of one printed circuit board to another. The electrical interconnect comprises a conductive conduit which extends beyond an edge of at least one printed circuit board. The conductive conduit is integrally formed with a conductive trace formed upon the printed circuit board(s). Thus, the conductive conduit which defines the electrical interconnect or the termination is essentially a conductive trace (which is preferably thicker than contemporary conductive traces) which extends beyond an edge of the printed circuit board, and thus extends off of the printed circuit board.
According to the preferred embodiment of the present invention, the electrical interconnects extend from one surface of the printed circuit board, while the conductive traces which electrically interconnect electronic components are formed upon the opposite side of the printed circuit board, so as facilitate fabrication of the comparatively thick electrical interconnects and the comparatively thin conductive traces using two separate conductive laminates of different thicknesses. However, as those skilled in the art will appreciate, the terminations may alternatively be formed upon the same side of the printed circuit board as the conductive traces. Indeed, both electrical interconnects and conductive traces may be formed upon either one or both sides of the printed circuit board, as desired.
A printed circuit board assembly is defined by a plurality of circuit boards and a plurality of electrical interconnects, wherein each electrical interconnect facilitates electrical communication between two of the printed circuit boards. Each electrical interconnect comprises a conductive conduit which extends beyond an edge of the two printed circuit boards.
As discussed below, the electrical interconnects of the present invention may be formed upon any desired layer of a multilayer printed circuit board. Thus, any desired layer of a multilayer printed circuit board may be used to either provide electrical interconnection to another printed circuit board or to define terminations, utilizing the electrical interconnects of the present invention.
The electrical interconnects of the present invention provide for both a robust, electrical interconnection between printed circuit boards which may be oriented substantially at any desired angle with respect to one another and provide robust electrical terminations for electrically connecting a printed circuit board or the like to another printed circuit board or to an electrical connector, wherein the terminations are defined integrally with the conductive traces formed upon the printed circuit board, so as to reduce manufacturing costs and so as to enhance the reliability of the terminations.